JWST images exoplanet surface, 30% larger than Earth

Astronomers have spent years using the James Webb Space Telescope to study exoplanet atmospheres. This result pushed that work a step further: into the rock itself. Using Webb’s mid-infrared instrument, a team led by Sebastian Zieba analyzed thermal emission from LHS 3844 b, a rocky planet about 30% larger than Earth, and found a surface best matched by dark, low-silica material such as basalt or other olivine-rich rock. (whbl.com) The data also pointed away from a detectable atmosphere, with upper limits that disfavor even trace amounts of carbon dioxide and sulfur dioxide. (arxiv.org) The planet, also known as Kua’kua, orbits a cool red dwarf about 48.5 light-years away in the constellation Indus. (arxiv.org) Its orbit lasts roughly 11 hours, and it is tidally locked, leaving one hemisphere in permanent daylight at about 1,000 Kelvin while the other remains far colder. Laura Kreidberg, managing director of the Max Planck Institute for Astronomy and senior author of the study, told Reuters the world is “a hellish, barren rock,” more like Mercury than Earth. ### How did Webb “see” a planet it cannot directly photograph? JWST did not produce a camera-style picture of LHS 3844 b. Instead, the researchers measured a 5-to-12 micron thermal emission spectrum — the planet’s infrared glow — and compared that signal with models of different rock types and surface textures. (arxiv.org) The University of Chicago, whose scientists were part of the collaboration, said the team used subtle changes in light as the planet moved through its orbit and passed behind its star. That “secondary eclipse” method let them isolate the planet’s own contribution to the system’s light and infer what kind of surface was producing it. (mpia.de) ### Why did scientists focus on LHS 3844 b? LHS 3844 b is one of the best available targets for this kind of measurement because it is both nearby and extremely hot. The planet circles very close to its star — roughly three stellar diameters above the star’s surface — making its dayside bright in infrared wavelengths that Webb can detect. (arxiv.org) A separate 2026 mass study described LHS 3844 b as “the most promising surface-characterization target known,” citing its strong emission signal for JWST observations. That combination of short orbital period, high temperature and relative proximity made it a test case for whether astronomers could move beyond atmosphere studies and start identifying exoplanet surface materials. (news.uchicago.edu) ### So is this actually a lava world? The new paper does not present LHS 3844 b as a globe covered by an active ocean of molten lava. The spectrum is best fit by a dark, old and likely space-weathered surface, and the authors said the data rule out fresh powdery surfaces while favoring basalt-like or olivine-rich material. (mpia.de) Max Planck Institute for Astronomy said the findings suggest prolonged geological inactivity, because the observations showed no evidence of accumulated volcanic gases. Penn State similarly described the crust as rocky and probably lacking much recent tectonic activity. (arxiv.org) ### What does the result change for exoplanet research? Sebastian Zieba and his co-authors wrote that JWST has opened “a new era” in the study of rocky exoplanets by enabling direct surface characterization with mid-infrared spectroscopy. Brandon Coy, a University of Chicago graduate student and co-author, said the technique can help scientists reconstruct how rocks formed and what processes shaped a planet over time. (arxiv.org) The study was accepted for publication in Nature Astronomy on April 8, according to the arXiv record, and the preprint was posted on April 30. The observations came from JWST program #1846, led by Kreidberg with co-principal investigator Renyu Hu, a project described as a search for signatures of volcanism and geodynamics on LHS 3844 b. (mpia.de) (arxiv.org)